$ { {-5} \times \left[\begin{array}{rr}{-1} & {-1} \\ {3} & {0} \\ {0} & {0}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-5}\times{-1} & {-5}\times{-1} \\ {-5}\times{3} & {-5}\times{0} \\ {-5}\times{0} & {-5}\times{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{5} & {5} \\ {-15} & {0} \\ {0} & {0}\end{array}\right]}$